1. Field of the Invention
The invention relates to a communication system, ports of the communication system and a method for managing a communication system, preferably to a synchronous communication system formed as a ring network of two or more ports coupled in daisy chain fashion to one another to allow communication.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
A communication system is generally known as a system that permits communication between nodes interconnected by a transmission line. Each node can transmit information and receive information across the transmission line. The communication system of interconnected nodes can be organized in various topologies, such as bus, ring, star, or tree topology or a combination thereof.
A bus topology network is generally regarded as linear. Transmissions from one node propagate along the transmission line and are received by all other nodes connected to that bus. A ring topology network, however, generally consists of a series of nodes connected to one another by unidirectional transmission links to form a single, closed loop. Examples of a ring network are described in IEEE 802.5 and Fiber Distributed Data Interface (FDDI).
The transmission line between nodes can be either wired or wireless, for example, copper wire, fiber optic, or wireless transmission medium for the chosen transmission line, respectively.
A communication system, for real-time applications or for transferring synchronous streaming data must have a low latency and a low transmission overhead.
Ethernet and IEEE 802.03 specify a particular protocol in which packets of data can be sent between computing systems. Ethernet can sense multiple access collisions and can arbitrate which source device will gain mastership over the transmission line. Ethernet operates at the lowest levels of the OSI reference model, normally reserved for the data link and physical link layers. The Ethernet protocol specifies a particular frame format of a preamble, followed by a destination address and a source address and then the data payload. The data is generally encoded in a 4B/5B or 8B/10B encoding structure prior to the data being sent across a coax or twisted pair transmission lines. On detection of a collision, a jam signal is transmitted to inform other nodes that a collision has occurred. A hub or a repeater will forward the jam signal on all ports, thereby informing all other nodes about the collision and forcing them to wait until the next transmission. The purpose of this jam signal is to extend a collision significantly, so that all other nodes on the network cease transmitting. Jamming is also used when dealing with congestion. It is an attempt to eliminate frame loss within a node by applying “back pressure” to other nodes consuming the node's buffer capacity. One way of accomplishing this is for a node to issue an Ethernet jam signal when buffers fill beyond a threshold level. Using the Ethernet jam signal makes a network rather indeterministic, as the forced delay for re-transmission is a minimum fixed delay permitting all other nodes to cease transmission plus a certain random delay time. Furthermore a single slow node can slow down the whole network.